International Patent Application Publication No. WO2009/027970 describes methods and devices (referred to herein as “proton/hydroxide injectors”) useful in producing local concentrations of protons or hydroxide ions, proton or hydroxide concentration gradients, and desired proton or hydroxide concentration topographies in an environment, such as an electrolyte solution, a gel, and the like. International Patent Application Publication No. WO2011/021195 and WO2011/021196 describe methods and devices for isoelectric focusing proton/hydroxide injectors and also describes display of data. Proton/hydroxide injector technology can be used to affect the pH of the whole solution or to create changes in the pH at specific position or for specific region.
Briefly, in some embodiments, the proton/hydroxide injector comprises a small compartment adjacent to a channel, with a Pt electrode dipped inside it, and a bipolar membrane separating the compartment from the channel. See, e.g., FIGS. 1A-1B. A bipolar membrane is an ion-exchange membrane having a structure in which a cation-exchange membrane and an anion-exchange membrane are joined together, and allows for water molecules to be split into protons and hydroxide ions. Voltage applied between the compartment and the channel divided by the bipolar membrane leads to water splitting and injection of protons or hydroxide ions into the channel. Some advantages of this technology can include, for example, bubble-free water hydrolysis and injection of generated ions directly to the channel, allowing short response time (e.g., if desired, below 1 minute).